If the quotation marks are really reliable, you could do it like this:

my @strings = (
   qq/Win32_Account.Domain="ADDomain",Name="aduser1"/,
   qq/Win32_Account.Domain="foobar",Name=""/,
   qq/Win32_Account.Domain="ADDomain",Name="aduser2"/,
  );

for ( @strings ) {
    my $user = join( "\\", (split /"/)[1,3] );
    $user = "Account Deleted" unless ( $user =~ /\S+\\\S+/ );
    print "$user\n";
}
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